Large tidal volumes at respiratory rates below 20 per minute are presently used for mechanical ventilation. There is no direct proof that these rats are optimum for positive pressure ventilation and not just an expression of technological limits of present respirators. In recent years, it has been shown by several groups of investigators, including ours, that good gas exchange can be achieved at much higher respiratory frequencies. This high frequency ventilation offers 1) superior gas exchange 2) with small tidal volumes, 3) at low intratracheal pressures 4) without circulatory impairment and 5) without interference with spontaneous breathing. High frequency jet ventilation (HFJV) introduced by us in 1975 offers additional advantage by using a small cannula introduced transtracheally or between the vocal cords instead by of endotracheal tube. For this method in our previous work a fluidic logic controlled ventilator was developed which is also capable of operating at high respiratory frequencies. In the proposed research, high frequency jet ventilation at respiratory rates between 100 and 600 per muinute will be studied on dogs to evaluate gas exchange in the lungs and determine the physiologic effects of HFJV on hemodynamics. The efficiency of HFJV will also be studied and the influence of changing inspiration/expiration ratio and catheter flow characteristics. HFJV synchronized with various phases of the heart action will also be evaluated. Finally, it will be studied whether HFJV can be applied transtracheally for long-term ventilation as an alternative to the indotracheal intubation. In clinical studies, the objective is 1) to evaluate the use of HFJV for weaning from respiratory support as an alternative to intermittent mandatory ventilation; 2) to study the application of HFJV through endotracheal tube for controlled ventilation in intubated patients requiring respiratory support.